rather can be used before negative adjectives to mean 'moderately'; it can also be used before positive adjectives to mean 'more than expected'
quite has a variety of meanings, ranging from 'moderately' to 'totally', depending on the tone of voice that is used.
Note that quite means 'fairly' before a gradable adjective. These are adjectives which can be modified, such as good, clever, helpful. Quite means 'completely' before an ungradable adjective. Ungradable adjectives are those which can't be modified, such as fantastic, brilliant, dreadful, etc.